In their contributions to Lewisian Themes, Rae Langton and Jonathan Schaffer both argue that quidditism -- the claim that possible worlds may differ only in which intrinsic properties play which causal/nomological roles -- does not entail skepticism about intrinsic natures because standard replies to skepticism about the external world carry over to skepticism about intrinsic natures.
But it seems to me that there is an important difference: if quidditism is true, we not only lack knowledge about intrinsic natures, but also any beliefs about them.
I have often encountered in articles, talks and classes the following argument for the necessity of true identity statements, always attributed to Kripke:
1) a = b (assumption)
2) ![$m[1]](/texer/images/?format=gif&fontsize=12pt&tex=%5CBox)
a = a
3) a = b (from 1, 2 by Leibniz' Law)
The argument is no good, and I think it is very doubtful that Kripke ever endorsed it.
On top of the Flüelapass
I'm back. Still not sure about the errors; something seems to be leaking memory here. I've turned a few things off, let's see if that helps.
Apparently something's wrong with my server causing it to randomly deliver 403 errors from time to time. I'm on my (roundabout) way back to Berlin and will investigate when I've arrived, probably on Monday. Until then apologies for the inconvenience.
I'm about to take the night train for my annual bike trip through the Alps. I will have internet access tomorrow, but then I'll be unreachable for about a week.
Suppose some thing x turns F, and a little later some other thing y turns G. x is the only F throughout history, so on a Humean account of laws of nature, it may well be just a coincidence that y's being G followed x's being F. Suppose it is.
But now consider another world just like this one except that in the far future, lots of G-turnings follow lots of F-turnings so that in this world, it is a law that whenever something turns F and another thing is suitably related, then that other thing turns G. In such a world, x's turning F caused y's turning G.
In section 24.D of his "Replies and systematic expositions" in the Schilpp volume, Carnap argues that every theory can be split into a component "representing the factual content of the theory", and another component serving as "analytic meaning postulates [...] for the theoretical terms". In fact, he doesn't speak about every theory, but it seems that what he says is true in general.
Take everything you believe about water, and call that your water theory. Your theory presumably contains things like "water fills our lakes and rivers", "water boils at around 100 °C under normal conditions", "water consists of H2O", and so on. All that is plainly empirical. Now the factual component of your theory, according to Carnap, is its Ramsey sentence: the theory with all occurrences of "water" replaced by a variable and prefixed by an existential quantifier binding that variable. The analytic meaning postulate then is the material conditional of the Ramsey sentence as antecedent and the theory itself as consequent. Let's call that the Carnap conditional of the theory.
Tim Williamson argues that no interesting conditions are such that if they obtain, then one is in a position to know that they obtain. I'll try to show that his argument fails for all conditions for which one can only non-inferentially believe that they obtain if they really do obtain. It seems to me that many interesting conditions -- probably including feeling cold and knowing that one feels cold -- are of this kind. I haven't checked the secondary literature, so what I'm going to say is probably old. Anyway, here goes.
There's been some comment spam here recently. I've made a few changes so that if your comment contains markup or an URL, you'll now have to confirm the (first) submission. Hope that doesn't cause any problems.
Long ago, I worried about how the Ramsey-Carnap-Lewis account of theoretical terms could be applied to predicates. I noticed two reasons why Lewis's proposal to just turn the predicates into singular terms ("Instead of [...] 'F ---', for instance, we can use '--- has F-hood'", HTDTT p.80) is no good: first, it entails that completely false theories, say about witches or gods, leave their theoretical predicates undefined, whereas in fact those predicates are clearly empty (and thus defined); second, the proposal can turn consistent theories into inconsistent theories. This second problem can be generalized: For many predicates, there is no corresponding property that could be denoted by a singular term. Exactly which predicates these are depends on one's theory of properties, but "having parts", "being self-identical", "being a set" and "being a property" are generally good candidates, besides of course "not instantiating oneself".